Probalistic reverse geocoding

ABSTRACT

The accuracy of a reverse geocode for a GPS fix in a mobile phone navigation device is improved significantly by considering together the user&#39;s last known location on an original route, the elapsed time between the last known location on the original route and the latest GPS fix, and the likelihood that the user could have travelled from the last known location on the original route to one of numerous candidate locations (generated from the reverse geocode) in the elapsed time. The navigation server relies only on a GPS fix, timestamps, and a back-end routing database to provide improved or superior accuracy of reverse geocoding a GPS fix (selection of a point on a road) when a relevant user has deviated from the intended route. The reverse geocoding allows for accurate and functional re-routing capabilities.

This application is a continuation of U.S. application Ser. No.12/588,143, entitled “Probalistic Reverse Geocoding,” filed on Oct. 6,2009, now U.S. Pat. No. 8,396,658; which claims priority from U.S.Provisional Application No. 61/136,805, entitled “Probabilistic ReverseGeocoding” to Barcklay, filed Oct. 6, 2008, the entirety of both areexplicitly incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to wireless communication. Moreparticularly it relates to route guidance (navigation) on a mobilewireless device including global positioning satellite (GPS) capability.

2. Background of Related Art

Navigation devices are typically GPS-based electronic systems used in avehicle to provide a real-time map of the vehicle's current location,together with step-by-step directions to a requested destination.

All navigation devices must handle the condition in which the userdeviates (leaves) their intended route. When this condition occurs, theapplication typically determines the user's current location by “reversegeocoding” the last GPS fix from the device. This new current locationis then used to generate a new route to the original destination.

Reverse geocoding is a process of returning an estimated position on astreet as it relates to a given latitude/longitude coordinate. Mobileapplications available today use a simple reverse geocoding algorithm tolocate the closest point on any road segment near the GPS coordinatereceived from the device.

However, due to the inherent inaccuracy of a GPS fix, this simplisticapproach may locate the user on an incorrect road that is near theuser's true location. Since this occurs while the user is driving andafter they have deviated from the intended route, the cost of anincorrect reverse geocode is quite high since the new route will also beincorrect.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, a method ofproviding an accurate location to a portable navigation device in acongested area when in an off-route condition comprises obtaining alatest location fix of the user's wireless navigation device, the latestlocation fix being off-route. A last known on-route location of a user'swireless navigation device is obtained. An elapsed time between the lastknown on-route location and the latest location fix is determined. Areverse geocode is performed on the latest location fix resulting in aplurality of potential location candidates. An estimated time of travelfrom the last known on-route location to each of the potential locationcandidates is determined, and a current location of the user's wirelessnavigation device is mapped as the potential location candidate having atravel time closest to the elapsed time.

A method of providing navigation server-based support for a wirelessnavigation device in accordance with another aspect of the inventioncomprises considering together a user wireless device's last knownon-route location, a latest GPS fix of the user's wireless device, andan elapsed time between the last known location on the original routeand the latest GPS fix. A likelihood that the user's wireless devicecould have travelled from the last known on-route location on theoriginal route to one of a plurality of candidate locations generatedfrom a reverse geocode, in the elapsed time, is determined. An estimatedtime of travel from the last known on-route location to each of theplurality of candidate locations is determined, and mapping informationis provided based on a current location of the user's wirelessnavigation device being determined as being the potential locationcandidate that has an estimated time of travel closest to the elapsedtime.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become apparent tothose skilled in the art from the following description with referenceto the drawings:

FIG. 1 shows an exemplary mobile phone including a user interfaceproviding route guidance navigation, as a user goes off route, inaccordance with the principles of the present invention.

FIG. 2 shows an exemplary method providing probabilistic reversegeocoding for a user of a mobile phone with an operating route guidancenavigation interface, in accordance with the principles of the presentinvention.

FIG. 3 shows a graphical depiction of a list of candidate reversegeocodes generated by a current GPS fix, each being a point on a roadsegment near the actual latitude/longitude, in accordance with theprinciples of the present invention.

FIGS. 4A to 4G show a route generated between the last known locationand each respective candidate reverse geocode result shown in FIG. 3.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Car navigation systems typically employ superior GPS technology, gyrosand actual vehicle speed to determine a vehicle's current position moreaccurately. But more recently navigation applications have becomeavailable on wireless phones. However, mobile phones don't have accessto a directly measured speed of a vehicle as do installed car navigationsystems. Moreover, the antenna of a mobile phone may not be in an idealposition as are the antennas for an installed car navigation system.While very good, inaccuracies in the measurement of a current locationmay lead to an erroneous mapping onto a road in a mobile phonenavigation application, particularly in areas where many roadsintersect. In a worse case, such inaccuracies can result in mapping of avehicle on a wrong road.

The present inventors have discovered that the accuracy of a reversegeocode can be improved significantly by considering together the user'slast known location on the original route, the elapsed time between thelast known location on the original route and the latest GPS fix, andthe likelihood that the user could have travelled from the last knownlocation on the original route to one of numerous candidate locations(generated from the reverse geocode) in the elapsed time.

The present invention provides an alternative approach to reversegeocoding that relies only on a GPS fix, timestamps, and a back-endrouting database. The present invention provides improved or superioraccuracy of reverse geocoding a GPS fix (selection of a point on a road)when a relevant user has deviated from the intended route. The reversegeocoding allows for accurate and functional re-routing capabilities.

FIG. 1 shows an exemplary mobile phone including a user interfaceproviding visual route guidance navigation, as a user goes off route, inaccordance with the principles of the present invention.

In particular, FIG. 1 depicts a mobile phone 120 providing visual routeguidance navigation to a user via a visual user interface including amobile phone display. In the disclosed embodiments, the user is presumedto be in an automobile, though the present invention relates equally totravel by way of any vehicle, including bicycles, bus, as well as travelby foot.

Though shown and described with respect to a visual user interface toguide a user of a mobile phone 120, the present invention relatesequally to audio route guidance and/or visual route guidance.

On the display of the mobile phone 120, a visual user interface displaysa map with relevant paths (e.g., roads in the case of vehicle travel).In the described situation, the user of the mobile phone 120 is carryingit with them while traveling in a car or bus as they approach an areacongested with roadways. The invention has particular applicability topoints at which one road passes over another, where a navigationapplication can easily get confused. In the given situation the user istraveling in a vehicle in an area near to quite a few roadways.

The triangular icon 402 depicts the vehicle in which the user istraveling, at its last known position of the mobile phone 120 as ittraveled along a route 406. In the shown example, the user was presentedwith, and was expected to travel along, a previously calculated route408. However, in the given scenario, the latest GPS fix puts the user ata point that would otherwise be considered to be along a differentroadway 410. The triangular icon 404 depicts the latest GPS position fixof a user as reported by the GPS device of the mobile phone 120 carriedby a passenger of a vehicle that was previously traveling along apreplanned route 408.

FIG. 2 shows an exemplary method providing probabilistic reversegeocoding for a user of a mobile phone with an operating route guidancenavigation interface, in accordance with the principles of the presentinvention.

In particular, as shown in FIG. 2, a mobile device 120 performs anavigation method supported by route guidance navigation informationprovided by a remote navigation server 140 within a phone network. Themobile device 120 communicates with the remote navigation server 140 viaan otherwise conventional wireless phone protocol.

The method for probabilistic geocoding in accordance with the principlesof the present invention begin with the following preferable input:

(a) Last known location on a road segment (map matched by theapplication) (While the user travels along a route, the application ‘mapmatches’ each GPS fix to the nearest point on the route. When thedistance to the nearest point exceeds some threshold, the user isconsidered off route.

(b) Timestamp of last known location.

(c) Current GPS fix (lat/lon) from the device.

(d) Timestamp of current GPS fix.

An exemplary method for probabilistic geocoding in accordance with theprinciples of the present invention is as follows:

In the mobile device 120, steps 202-208 are performed in the exemplaryembodiment, whereas steps 302-316 are performed at a suitable navigationserver 140 in the exemplary embodiment.

In step 202 of the mobile device 120, the mobile phone 120 determines orotherwise obtains information informing it that it is ‘off-route’.

In step 204, a new route request is created.

In step 206, the new route request is sent to the navigation server 140.

In step 208, after the navigation server 140 provides a new route backto the mobile phone 120, guidance is started on the new route receivedback from the navigation server 140.

The navigation server 140 receives a new route request from the mobilephone 120 in step 302.

In step 304, the navigation server 140 determines candidate locations.The navigation server 140 also examines the road network proximate tothe latest GPS fix position. The navigation server 140 also selectspoints on nearest road links within a given error radius of the GPS fix.

In step 306, the navigation server 140 determines if there are more thanone candidate location, or road presence point, within a given errorradius of the latest GPS fix. A list of candidate reverse geocodelocation results is generated from the current GPS fix 404. Eachcandidate location is a point on a road segment near the actuallatitude/longitude.

FIG. 3 shows a graphical depiction of a list of candidate reversegeocodes generated by a current GPS fix, each being a point on a roadsegment near the actual latitude/longitude, in accordance with theprinciples of the present invention.

In particular, as shown in FIG. 3, a latest GPS fix is depicted by thetriangular icon 404. However, in the given example, at least 6 candidatelocations 502-512 are identified by the navigation server 140.

Referring back to FIG. 2, in step 308, for each candidate location, aroute is generated for each candidate location, from the last knownlocation 406, to the respective candidate location.

FIGS. 4A to 4G show a route generated between the last known locationand each respective candidate reverse geocode result shown in FIG. 3.

In particular, FIG. 4A depicts a route to get to location candidate 510from the last known position 402. FIG. 4B depicts a route to get tolocation candidate 512 from the last known position 402. FIG. 4C depictsa route to get to location candidate 502 from the last known position402. FIG. 4D depicts a route to get to location candidate 508 from thelast known position 402. FIG. 4E depicts a route to get to locationcandidate 506 from the last known position 402. FIG. 4F depicts a routeto get to location candidate 504 from the last known position 402. FIG.4G depicts a route to get to location candidate 514 from the last knowposition 402.

For each candidate reverse geocode result, a route is generated betweenthe last known location 402 and the respective candidate location502-514. This route generation step calculates estimated elapsed timebased on the speed limit of each road segment traveled. The presentinvention also contemplates that other influences such as trafficimpacts may be taken into account, e.g., the presence and duty cycle oftraffic lights along the way, stop signs, etc.

Referring back to FIG. 2, in step 310, for each route to respectivecandidate locations calculated in step 308, the travel time isdetermined, and compared to an elapsed time between the time stamp ofthe last known location 406 and the time stamp of the latest GPS fix404.

The location candidates 502-514 are ranked based on the elapsed timebetween the two GPS fixes 402 and 404, and the estimated time of travelbetween the known and current location.

The travel time for each route is generally the driving distance on eachroad segment×the speed limit on each road segment. For simplicitypurposes of the given embodiment shown in FIGS. 4A to 4G, it is presumedthat the speed limit is the same on all shown roads.

In step 312, a best fit candidate location is selected as a candidatelocation having a time closest to an expected time since the last knownlocation was fixed. Thus, the location candidate with the smallest timedifference is selected and returned as the reverse geocode result. Giventhe presumption above about a same speed limit on all shown roads inthis example, the candidate location shown in FIG. 4G is a best fit.

Referring back to FIG. 2, in step 314, a new route is calculated fromthe latest or current location fix 404, to the original destination.

Finally, in step 316, the new route is communicated to the client mobilephone 120.

The present invention may be generalized further to find a best-fitroute between a series of 2 or more points, in accordance with theprinciples of the present invention. In this case, there is not a lastknown location but pairs of candidates from which the most likely routemay be selected. This would be more computationally intensive but can beused to improve the accuracy of reverse geocoding (of a moving device)when there is no last known location.

The invention may also be generalized by maintaining an ongoing list oflikely reverse geocode results. For each subsequent GPS fix, theprevious list may be used to generate the new list. This may be employedeven when not on a route.

The present invention has particular application to navigationapplication providers.

While the invention has been described with reference to the exemplaryembodiments thereof, those skilled in the art will be able to makevarious modifications to the described embodiments of the inventionwithout departing from the true spirit and scope of the invention.

What is claimed is:
 1. A method of providing an accurate location to auser's wireless navigation device, comprising: receiving a route requestfrom a user's wireless navigation device; obtaining a last knownon-route location of said navigation device; obtaining a latest locationfix of said navigation device; performing a reverse geocode on saidlatest location fix to determine a plurality of candidate locationswithin a given error radius of said latest location fix associated withsaid navigation device; determining an estimated time of travel betweeneach of said plurality of candidate locations and said last knownon-route location; and returning a most likely candidate location, fromsaid plurality of candidate locations, based on a closest match betweensaid respective estimated times, and an elapsed time between said lastknown on-route location and said latest location fix.
 2. The method ofproviding an accurate location to a user's wireless navigation deviceaccording to claim 1, wherein: said latest location fix is a GlobalPositioning System (GPS) fix.
 3. The method of providing an accuratelocation to a user's wireless navigation device according to claim 1,wherein: said navigation device calculates a new route from a currentlocation of said navigation device and said returned most likelycandidate location.
 4. The method of providing an accurate location to auser's wireless navigation device according to claim 1, wherein: saidnavigation device is a portable navigation device.
 5. The method ofproviding an accurate location to a user's wireless navigation deviceaccording to claim 1, wherein: said navigation device is a wirelessphone.
 6. The method of providing an accurate location to a user'swireless navigation device according to claim 1, wherein: generation ofsaid plurality of candidate locations is based on a speed limit of eachroad segment traveled.
 7. The method of providing an accurate locationto a user's wireless navigation device according to claim 1, wherein:said plurality of candidate locations is based on traffic.
 8. The methodof providing an accurate location to a user's wireless navigation deviceaccording to claim 1, wherein: said plurality of candidate locations isbased on a duty cycle of a traffic light.
 9. The method of providing anaccurate location to a user's wireless navigation device according toclaim 1, wherein: a same speed limit is used for determining saidestimated time of travel between each of said plurality of candidatelocations and said last known on-route location.